Much of our knowledge of verterbrate photoreceptor function results from intracellular recordings made in the retinas of ectotherms ("cold-blooded" organisms). For experimentation, these so-called "lower vertebrates" offer many technical advantages which make them the animals of choice for detailed studies of photoreceptor physiology. However, well known inter-species differences in the details of retinal morphology, physiology, and organization raise the question of the applicability of knowledge gained through studies of ectotherms to our understanding of mammalian retinas. This project proposes a direct study of the physiological properties of mammalian photoreceptors. It is believed that application of newly developed technical advances, which are available in this laboratory and which greatly facilitate work in small cells, will permit intracellular recordings to be made from mammalian photoreceptor coupling, and interactions between photoreceptor and horizontal cells in the rabbit retina. This retina has been selected because of its demonstrated viability when maintained as an isolated, perfused tissue, and because of its wealth of morphologically demonstrated receptor cell interconnections. Such interconnections are similar to junctions seen between primate photoreceptors as well as those between photoreceptors known to be functionally interconnected in other species. Additional experiments will be performed on the cone-dominated retina of the tree shrew Tupia glis, a diurnal primate which displays visual acuity comparable to that of man. All work with rabbits and tree shrews will be preliminary to conducting such experiments in higher primates as soon as possible. This work will be of benefit in improving our understanding of the physiology and organization of the human retina and in selecting appropriate model systems for detailed studies of primate photoreceptor physiology.